The conditions of roads which vehicles pass through are changed by, for example, opening of a new expressway or a new bypass road or closing a road by construction or a disaster. It is necessary to reflect such opening and closing of roads on map data as quickly as possible. Especially with the recent spread of navigation systems including car navigation systems, earlier update of map data has been highly demanded.
Various techniques have been proposed to detect a change of the road conditions by using information sent from vehicles called probe cars which actually run through roads and enable earlier update of road network data. For example, when a plurality of probe cars (vehicles) pass through a location which has been unregistered as a road, one proposed technique registers the location in a map database, in order to enable earlier reflection of a change in road network on the map database (e.g., JP H09-243391A).
This proposed technique, however, registers the location which has been unregistered as a road in the map database, based on the frequency when probe cars pass through. This technique does not identify the importance of a change of the road conditions, especially the significance of influence on road users. It is impossible to obtain all pieces of information which are to be registered in the map database, from only the information sent from probe cars. Generally investigators are dispatched for survey and registration of detailed data. There is accordingly a demand that surveys on changes of the road conditions are made in order of importance. The prior art technique cannot, however, meet this demand.
A proposed road network analysis system (e.g., JP 2012-150016A) is the excellent technique that processes probe information obtained from, for example, probe cars and extracts a change in traffic amount to find an important change in road network as early as possible. A change in traffic amount is, however, also caused by, for example, opening or closing of a large commercial facility. Further improvement of the detection accuracy is accordingly demanded.